In the design of elastomeric bearings, why are steel plates inserted inside the bearings?

For elastomeric bearing to function as a soft spring, the bearing should be allowed for
bulging laterally and the compression stiffness can be increased by limiting the amount of
lateral bulging. To increase the compression stiffness of elastomeric bearings, metal plates
are inserted. After the addition of steel plates, the freedom to bulge is restricted and the
deflection is reduced when compared with bearings without any steel plates under the same
load. Tensile stresses are induced in these steel plates during their action in limiting the
bulging of the elastomer. This in turn would limit the thickness of the steel plates.
However, the presence of metal plates does not affect the shear stiffness of the elastomeric
bearings.